LEDs have a higher efficiency and a longer lifetime than incandescent lamps and halogen lamps. In the field of LEDs, vigorous researches have recently been conducted to use white LEDs for lighting, as white LEDs with higher luminance have been developed. A common white LED at present includes a combination of an LED bare chip emitting blue light and a phosphor excited by the blue light to emit yellow light, so that the blue light and the yellow light mix together to generate white light.
A manufacturing method of this white LED includes a wafer fabrication process in which the LED bare chip is obtained and an assembly process in which the LED bare chip is packaged.
In the wafer fabrication process, the LED bare chip is typically obtained by forming a multilayer epitaxial structure including a light emitting layer on a light-transmitting substrate, such as a sapphire substrate by epitaxial growth. In addition, an anode electrode and a cathode electrode are formed on a main surface of the multilayer epitaxial structure which faces away from the sapphire substrate.
In the assembly process, the LED bare chip is mounted on a lead frame, a printed-wiring board or the like since the LED bare chip alone can not be put to use. After this, a resin mixed with a phosphor material is dropped onto the mounted LED bare chip and cured, to form a phosphor film. Subsequently, steps such as molding a periphery of the phosphor film using a resin are conducted to complete the white LED. The completed white LED is tested for its electrical and optical performance before shipped.
However, there is a high possibility that the white LED manufactured in the above-descried manner has poor optical performance. The reason is explained in the following. Firstly, the phosphor film is formed in such a manner that the resin mixed with the phosphor material is dropped onto the LED bare chip and then cured. Therefore, it is highly likely that the thickness of the phosphor film in the white LED is not equal to a designed thickness. Here, a color temperature of the white light emitted by the white LED is determined by a ratio between a quantity of the blue light and a quantity of the yellow light. This being so, if the phosphor film is thick, the quantity of the blue light is small and the quantity of the yellow light is large, so that white light of a low color temperature is produced. On the other hand, if the phosphor film is thin, white light of a high color temperature is produced. Consequently, a desired color temperature can not be realized. Secondly, the phosphor film tends to be formed at an uneven thickness. If the phosphor film is formed at an inappropriately uneven thickness, unevenness of color occurs.
White LEDs with the above-mentioned defects are rejected as a result of the optical performance test. This results in a low ratio of accepted finished products (white LEDs) to all finished products.
In an attempt to improve the ratio of accepted finished products, it has been proposed to test white LEDs for unevenness of color prior to the assembly process. This proposal has been realized by an LED chip that is disclosed in Japanese patent No. 3399440.
According to this disclosure, an LED bare chip is mounted on a substrate (an auxiliary mounting substrate) that has a slightly larger surface area than the LED bare chip, with a multilayer epitaxial structure facing downwards (i.e. a sapphire substrate of the LED bare chip faces upwards). A phosphor film is then formed on and around the LED bare chip mounted on the auxiliary mounting substrate. Thus, this LED bare chip can be tested for its optical performance prior to an assembly process in which the LED bare chip is mounted on a lead frame or a printed-wiring board. As a consequence, the ratio of accepted finished products can be improved.
However, the LED chip disclosed in the Japanese patent No. 3399440 has an extra constituent, i.e. the auxiliary mounting substrate. Accordingly, an entire thickness (height) of the LED chip increases by a thickness of the auxiliary mounting substrate, which results in an increase in chip size.
In light of the above-described problems, an object of the present invention is to provide a semiconductor light emitting device which can be tested for its optical performance before packaged without increasing a size of the semiconductor light emitting device. The object includes provision of a manufacturing method of the semiconductor light emitting device, and a light emitting module, a lighting apparatus and a display element using the semiconductor light emitting device.